Comparative Study to Examine Whether Echocardiography Performed During Cardiac Resynchronization Therapy Device Implantation Can Improve the Response Rate

Inclusion Criteria: 1. Patients with SR or AF, indicated for CRT procedures (NYHA Class III or ambulatory Class IV despite optimal medical therapy, QRSd≥120ms and LVEF≤35%) 2. Patients with ischaemic or non-ischaemic cardiomyopathy can be recruited Exclusion Criteria: 1. Patients already implanted with an implantable cardiac device, undergoing device upgrade or generator replacement 2. Patients who aged less than 18 or over 80. 3. Patients who are pregnant. 4. Patients who cannot give informed consent. 5. Patients who are judged to have severe mental impairment and cannot report symptoms of heart failure during follow-up. 6. Patients who have comorbid congenital heart disease. 7. Patients who have severe valvular heart disease, apart from severe mitral regurgitation. 8. Patients who have unstable angina or who are within 1 month of myocardial infarction. 9. Patients who have severe lung disease and accurate clinical assessment for heart failure symptoms cannot be performed. 10. Patients who have poor echocardiographic windows precluding reliable echocardiographic examination during baseline assessment, CRT procedures or follow-up.